A GaN-based Schottky barrier diode (GaN-SBD: Schottky barrier diode) is expected, because of its physical characteristic, to be applied to a server system and the like as a device having a high breakdown voltage and capable of performing high-speed operation. In order to reduce an energy loss in a GaN-SBD, it is important to lower an on-resistance and a forward voltage. For lowering the on-resistance and the forward voltage, it is effective to lower a work function of an anode electrode (Schottky electrode). Meanwhile, the work function of the anode electrode and the backward breakdown voltage are in a tradeoff relation. Therefore, when the work function of the anode electrode is lowered to lower the on-resistance and the forward voltage, the backward breakdown voltage is lowered.
For the realization of high breakdown voltage, there has been proposed a structure in which an Mg-doped p-type GaN layer is provided between an outer peripheral portion of an anode electrode and an n-type GaN layer which forms a Schottky junction with the anode electrode. In order to obtain the structure, there is a need to form a p-type GaN layer on an n-type GaN layer, perform patterning of the p-type GaN layer by dry etching to expose a front surface (Schottky surface) of the n-type GaN layer, and form an anode electrode on the Schottky surface.
However, Mg is difficult to be activated, and even if activation annealing is performed at 1000° C. or higher, only about 1% of a doped amount is activated. For this reason, when forming the p-type GaN layer, in order to sufficiently secure activated Mg, there is a need to dope a large amount of Mg of 1×1019 cm−3 or more, and perform activation annealing at 1000° C. or higher. When the large amount of Mg is doped, crystallinity of the p-type GaN layer is easily reduced. Further, a roughness of a Schottky surface of an n-type GaN layer, which is exposed after performing patterning of the p-type GaN layer, is easily caused, resulting in that the yield is easily reduced. Further, when performing dry etching, a roughness of the p-type GaN layer itself is easily caused. For this reason, it is extremely difficult to realize the practical application of the structure in which the Mg-doped p-type GaN layer is provided.    Patent Literature 1: Japanese Laid-open Patent Publication No. 2008-177369    Patent Literature 2: Japanese Laid-open Patent Publication No. 2010-40698